Diffusion-limited deposition with dipolar interactions: fractal dimension and multifractal structure

Computer simulations are used to generate two-dimensional diffusion-limited deposits of dipoles. The structure of these deposits is analyzed by measuring some global quantities: the density of the deposit and the lateral correlation function at a given height, the mean height of the upper surface for a given number of deposited particles and the interfacial width at a given height. Evidences are given that the fractal dimension of the deposits remains constant as the deposition proceeds, independently of the dipolar strength. These same deposits are used to obtain the growth probability measure through Monte Carlo techniques. It is found that the distribution of growth probabilities obeys multifractal scaling, i.e. it can be analyzed in terms of its $f(\alpha)$ multifractal spectrum. For low dipolar strengths, the $f(\alpha)$ spectrum is similar to that of diffusion-limited aggregation. Our results suggest that for increasing dipolar strength both the minimal local growth exponent $\alpha_{min}$ and the information dimension $D_1$ decrease, while the fractal dimension remains the same.Comment: 10 pages, 7 figure

Diffusion-limited deposition of dipolar particles

Deposits of dipolar particles are investigated by means of extensive Monte Carlo simulations. We found that the effect of the interactions is described by an initial, non-universal, scaling regime characterized by orientationally ordered deposits. In the dipolar regime, the order and geometry of the clusters depend on the strength of the interactions and the magnetic properties are tunable by controlling the growth conditions. At later stages, the growth is dominated by thermal effects and the diffusion-limited universal regime obtains, at finite temperatures. At low temperatures the crossover size increases exponentially as T decreases and at T=0 only the dipolar regime is observed.Comment: 5 pages, 4 figure

Bilepton effects on the WWV^* vertex in the 331 model with right-handed neutrinos via a SU_L(2)XU_Y(1) covariant quantization scheme

In a recent paper, we investigated the effects of the massive charged gauge bosons (bileptons) predicted by the minimal 331 model on the off-shell vertex WWV^* (V=gamma, Z) using a SU_L(2) X U_Y(1) covariant gauge-fixing term for the bileptons. We proceed along the same lines and calculate the effects of the gauge bosons predicted by the 331 model with right-handed neutrinos. It is found that the bilepton effects on the WWV^* vertex are of the same order of magnitude than those arising from the SM and several of its extensions, provided that the bilepton mass is of the order of a few hundred of GeVs. For heavier bileptons, their effects on the WWV^* vertex are negligible. The behavior of the form factors at high energies is also discussed as it is a reflect of the gauge invariance and gauge independence of the WWV^* Green function obtained via our quantization method.Comment: Replaced to match published versio

New forms of local governance : a theoretical and empirical analysis of municipal corporations in Portugal

What factors influence local governments to rely on municipal corporations to provide public services? This article seeks to identify which factors lead local governments to use local corporate public sector organizations, particularly municipal corporations, for service delivery. Based on the ideas of the neo-institutionalism approach to public administration developed by Murray Horn (1995), we argue that local officials trade-off bureaucratic costs of in-house production with agency costs of external delegation to municipal corporations when deciding how to deliver local public services. Econometric models are employed to test this explanation for the adoption of municipal corporations by the 278 Portuguese local governments. The results indicate that organizational size, financial independency, and fiscal surplus, as well as ideological concerns and the activity of local interest groups, drive choices of local governance structures.Fundação para a Ciência e a Tecnologia (FCT

New forms of local governance: a theoretical and empirical analysis of the case of Portuguese Municipal Corporations

This paper is an attempt to identify which factors influence Portuguese local governments to rely on municipal corporations to provide public services. Based on the ideas of the new institutional economics applied to public administration developed by Milgrom and Roberts (1990) and Horn (1995), we argue that influence costs of in-house production and bargaining costs of external delegation to municipal enterprises are the main determinants of the creation of municipal corporations and other types of local public sector organizations external to the local government. An event count model is employed to explain the differences across 278 Portuguese local governments in adopting municipal corporations/enterprises. Results indicate that organizational size, financial dependency, and fiscal stress, as well as ideological concerns and the activity of local interest groups drive the choices of local governance structures

Understanding intergovernmental cooperation in a context of devolution: an empirical study of collaboration among portuguese municipalities

Why do local governments engage in formal cooperative agreements to deliver municipal services? What are the determinants of these collaborative efforts? We review the literature on horizontal collaboration and intergovernmental relations developed by the political economy, public choice, institutional collective action, and network literatures and present a theoretical model that intertwines several arguments from these literatures. The theoretical model suggests that the decision to collaborate is a product of prior experiences of competition/cooperation between municipal governments, the incentives for efficiency gains derived from cooperation, and the institutional setting in which intergovernmental relations take place. Based on this theoretical model and using a research design inspired by the literatures on international conflicts and coalition governments, we develop and test a series of hypotheses concerning the decision to cooperate by Portuguese municipal governments in face of recent decentralization trends. We find support for our trust and centrality hypotheses as incentives to cooperation, but fragmentation within local governments poses a constraint to collaborative efforts between municipalities.Fundação para a Ciência e a Tecnologia (FCT)

Static quantities of a neutral bilepton in the 331 model with right-handed neutrinos

A neutral vector boson can possess static electromagnetic properties provided that the associated field is no self-conjugate. This possibility is explored in the $SU_C(3) X SU_L(3) X U_N(1)$ model with right-handed neutrinos, which predicts a complex neutral gauge boson $Y^0$ in a nontrivial representation of the electroweak group. In this model the only nonvanishing form factors are the CP-even ones, which arise from both the quark and gauge sectors, and contribute to the magnetic dipole and the electric quadrupole moments of this neutral particle.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Climate Change Threats to Semi-Arid Transhumance Grazing Systems: Proposals for Adaptation in Cabo Verde

Global warming has changed the rainfall regime in the Sahelian region, endangering and widespread poverty and chronic famines in Cape Verde, where rural communities\u27 well-being and food security depend on rainy agriculture. Local responses to rainfall new patterns and scarcity have been livestock reduction with significant revenue losses. Together with dry mist occurrences, these environmental constraints demand to define priority actions to adapt and mitigate climate change\u27s direct impacts. According to fifty household inquiries, this work explains the transhumant grazing practices on a semi-arid plateau in Tarrafal (Santiago, Cabo Verde), prospecting adaptation alternatives for sustainability. We related grazing patterns and pastoral infrastructures to the household\u27s socioeconomics, analyzing the livestock system - composition and management - and their relationship to rangeland utilization. Livestock of male-headed households is different from female-headed ones, mainly cattle in the firsts and goats in the lasts. Herds decreased during the 2016-2018 drought, including equine that lost interest in supporting farmers that abandoned the most remote agriculture patches. Based on a carrying capacity zoning, the geographical analysis assessed existing water supply structures\u27 suitability and designated new ones to improve transhumance effectiveness. New watering points along principal depressions allow to establish forage species - Parkinsonia aculeata, Opuntia ficus-indica, Pannisetum pedicellatum, and Desmanthus virgathus – and reduce stormwater runoff. It also means to improve natural resources by biodiversity conservation and wildlife management. These and other proposals could sustain and adapt the Tarrafal transhumant grazing system to climate change, reduce the farmers\u27 income loss, and improve food security